1. Field of the Invention
This invention relates to trunked radio communication systems, particularly to data-overlaid trunked radio communication systems.
2. Description of the Background Art
Trunked radio communication systems provide simplex or half-duplex mode radio communication, typically of analog voice information, between base and mobile units over a particular geographical area through a group, or "trunk," of associated radio channels. Thus, when a transmission is made over a radio channel associated with a given trunk, base and mobile units that are tuned to other radio channels also associated with that trunk may receive the same transmission.
Due in part, however, to the intermittent nature of transmitted voice conversations, significant voice channel capacity sometimes remains unused during normal operation of trunked radio systems. Moreover, because trunked radio systems are designed primarily for handling analog voice data, trunked radio systems are not well-suited for communicating digital data, particularly data packets, frames or datagrams, according to standard digital communications protocol.
Therefore, it would be desirable to improve existing voice-based trunked radio infrastructures by overlaying thereon a data communication system for sending and receiving digital data information over unused radio channel capacity.